Continuous pulping process for the production of paper products



March l2, 1963 H. R. AMBUEHL ETAL 3,081,218

CONTINUOUS PULPING PROCESS FOR THE PRODUCTION OF PAPER PRODUCTS FiledMarch 18, 1960 United States Patent OM Fla.

Filed Mar. 18, 1960, Ser. No. 15,993 Claims. (Cl. 162-19) This inventionrelates to a continuous pulping process for the production of paperproducts, and has particular applicability to a process for the pulpingof sugar cane bagasse or other similar fibrous, non-woody,ligne-cellulose containing plantY materials for the manufacture ofnewsprint or other paper products.

A primary object of this invention is the provision of an improvedprocess for the continuous production of pulp from bagasse or similarmaterial which results in a pulp of exceptionally strong character whichis readily bleachable and suitable for use in the production of paperswith a high furnish content up to and including 100% pulp Ifurnish.

A further object of the invention is the provision of a continuousprocess wherein continuous control of the cooking and reactionconditions may be continuously provided, resulting in obtaining themaximum strength in the finished material with a minimum degradation ofthe cellulose.

A further important object of this invention is the provision of acontinuous process of this character which will employ the commonly usedpresently existing apparatus.

A still further object of the invention is the provision of such aprocess which is extremely low in cost and relatively rapid.

A further important object of the invention resides in the provision ofa process wherein a certain amount of the pith is retained in theprocessed material, in contrast to the prior art wherein all or most ofthe pith has hitherto been removed, such pith retention resulting in theimproved quality of the end product.

A still further specific object of the invention is in the provision ofa process including the step of aqueous digestion with an agentcontaining NaOH alone or in combination with NaZS, or elemental sulfur.

A further and still more specic object of the invention resides in theprovision of a process wherein the material to be pulped is initiallypassed over a vibrating screen` for the purpose of removing a portion ofthe dirt,

dust and pith-type material, and subsequently treated in a continuousdigester and pre-hydrolyzed. The pre-hydrolyzed material is subsequentlyblown into a cyclone where it is sprayed with water and discharged fromthe cyclone onto a de-watering conveyer where more water may be added ifnecessary. The de-watered material is then passed to a press, andsubsequently to a shredding device where it is de-compressed for analkaline cooking stage. This alkaline cooking stage is accomplished byheat treating the material in a continuous digester with an aqueousdigesting agent which contains NaOH alone or in combination with Na2S orelemental sulfur. It is then ready for use. The particular times andtemperatures as well as other essential elements of the preceding stepsof the process will be more fully discussed hereinafter.

Still other objects of the invention reside in the provision of thespecific times, temperatures, conditions, steps and sequence ofoperation all as will be more fully described hereinafter.

The single FIGURE of the drawing is a schematic flow diagram disclosingthe various steps of the process in accordance with the instantinvention.

ICC 3,081,218

Patented Mar. 12, 1963 Referring now to the particular process indetail, bagasse from a sugar mill, or a storage area, or other suitablesimilar material of non-woody, ligne-cellulose containing plantsubstance is first passed over a vibrating screen. The material isscreened in such manner that not less than 2% nor more than 30% of thedirt, dust and pithtype material is removed. Such screened material maybe utilized for steam generation, or for any other purpose yfor which itis suitable. t

In the second step of the process the screened material is passed to acontinuous digester where it is prehydrolyzed at a temperature of notless than C. nor more than C., for not less than five minutes nor morethan fifty minutes. This step results in obtaining the maximum strengthin the linished material with a minimum of degradation of the cellulose.In this pre-hydrolysis step the moisture content is maintained at notless than 65% nor more than 90% by weight of the raw material. Thepre-hydrolysis stage permits the material to be heated in its own acidstate and by controlling the reaction permits the reduction of the pithand pentosan contents in this and the succeeding steps.

The pre-hydrolyzed material is passed from the con-4 tinuous digesterinto a blow cyclone, where it is sprayed with water as it is dischargedfrom the cyclone onto a de-watering conveyor. On this conveyer morewater may be added if necessary to maintain a consistency of not lessthan 3% or more than 20% by weight of oven dry material. A wide moisturerange is needed here due to the variations in the age or other conditionof the raw material and subsequently the amount of washing for removalof the pre-hydrolysis step liquors.

The de-watered material is then passed to a press where the consistencyis increased to an oven dry percentage of not less than 15% nor morethan 60%. The wide variation in compression permits the use of most ofthe pressing equipment which is currently on the market.

The fifth step of the operation consists in passing the pressed materialto a shredder where it is decompressed by shredding for the next oralkaline cooking stage.

The sixth step or alkaline cooking comprises `a very important elementof this process, and in this step the deeompressed condition shreddedmaterial is passed to a second continuous digester along with an aqueousdigesting agent which may contain NaOH alone, or in combination withNa2S or elemental sulfur. The ratio of the cooking agent to oven dryplant material is not less than 2 to l nor more than l2 to l. Thecombined amount of alkaline cooking agent chemicals based on the ovendry weight of the plant material is to be not less than 5% nor more than20%, and will have a suliidity content of 0% to 35%.

The material is heated under pressure in a blow tank to a temperature ofnot less than 105 C. nor more than 190 C., and is retained at thistemperature for not less than 4 minutes nor more than 30 minutes. Afterthis operation the material is passed to the washers, and is then readyfor use.

In` the process hereinbefore described variations in temperature andtime, as well as consistency and quantity of materials have been setout, wherein the process is applicable within the limits defined. Theselimits will vary as above stated in accordance with the condition andpurity of the material.

It has been found, however, that when using, for example two-year-oldbagasse, 100% bagasse pulp has been furnished to a Fourdrinier papermachine to produce commercial grades of salable paper under thefollowing specialized conditions. In the rst step of the process 3% ofthe dirt, dust and pith-type material has been removed, and in thesecond step the pre-hydrolyzation has been preferably achieved at atemperature of 165 C. for a time of 30 minutes, with a moisture contentof 76%. The treatment in step 3 in the blow cyclone has beenaccomplished at a consistency of 11% by Weight of oven dry material. Inthe fourth step the pressing has been effected to a consistency of anoven dry percentage of 36%. The time of the shredding operation of step5 is immaterial, and it is continued to completion. In step No. 6 adesirable condition exists where the ratio of the cooking agent to theoven dry plant material is 9 to 1, the sulidity is 27.7% when utilizingNaOH and NazS, and the combined amount of the alkaline cooking agentchemicalswbased on the oven dry weight of the plant material is 13.6%.

This step is achieved at a temperature of 160 C. for a period of 18minutes.

The above-described specic process is merely illustrative of one of themore highly desirable combinations or arrangements that are achieved bythe process of this inventive concept.

From the foregoing it will now be seen that there is herein provided animproved process for the continuous pulping of 100% sugar cane bagasse,or other similar fibrous, non-woody, ligno-cellulose containing plantmatcrials, which produces a highly satisfactory, exceptionally strong,readily bleachable pulp which may be employed in the production of suchpaper products as newsprint or the like.

As many embodiments may be made of this inventive concept, and as manymodiiications may be made in the embodiment hereinbefore shown anddescribed, it is to be understood that all matter herein is to beinterpreted merely as illustrative, and not in a limiting sense.

We claim:

. 1. A continuous process for pulping of brous, nonwoody,ligno-cellulose containing plant materials which comprises the steps ofscreening the material to remove a proportion of the dirt, dust andpith-type material therein; pre-hydrolyzing the screened material with amoisture content by Weight of oven dry material of from 65 to 90% fornot less than five minutes nor more than 50 minutes at a temperature notless than 140 C. and not more than 190 C.; spraying the pre-hydrolyzedmaterial in a blow cyclone; de-moisturizing the material; compressingthe material and subsequently shredding the compressed material; passingthe completely shredded decompressed conditioned material to acontinuous digester along with an aqueous digesting agent containingNaOH; and iinally, digesting the material, at a temperature of not lessthan 150 C. nor more than a 190 C. for not less than four minutes normore than thirty minutes.

2. The process of claim 1 wherein the aqueous digesting agent includeselemental sulfur.

3. The process of claim 1 wherein the aqueous digesting agent containsNaOH.

4. The process of claim 1 wherein the aqueous digesting agent containsNazS. l

5. The process of claim 1 wherein the aqueous digesting agent comprisesNa2S plus NaOH with a sultdity content of approximately 27.7%.

6. The process of claim 1 wherein the fibrous plant material comprisessugar can bagasse.

7. A continuous process for pulping fibrous, nonwoody, ligno-cellulosecontaining plant materials which comprises the steps of screening thematerial to remove 2% to 30% of the dirt, dust and pith-type materialtherein; pre-hydrolyzing the screened material at a temperature of notless than 140 C. and not more than 190 C. for not less than 5 minutesnor more than 50 minutes with a moisture content by weight of oven drymaterial of from to 90%; spraying the pre-hydrolyzed material in a blowcyclone, moisturizing the material to maintain a consistency of not lessthan 3% nor more than 20% by weight of oven dry material, compressingthe material to increase the consistency to not less than 15% nor morethan 60% by weight of oven dry material, subsequently shredding thecompressed material, passing the material through an alkaline cookingstep in a continuous digester with an aqueous digesting agent containingNaOH in a ratio of not less than 2 to 1 and not more than 12 to 1 withthe amount of continuous digester chemical based on the oven dry weightof plant material not less than 5% nor more than 20%, and having asuliidity content of 0% to 35%, and the material is digested at atemperature of not less than C. nor more than 190 C. for not less than 4minutes, nor more than 30 minutes.

8. The process of claim 7 wherein the continuous digester contains NaOHand NazS.

9. The process of claim 7 wherein the continuous digester containselemental sulfur.

10. A continuous process for pulping of brous bagasse from sugar canewhich comprises the steps of screening the bagasse to removesubstantially 3% of the dirt, dust and pith-type material therein,prehydrolyzing the screened material with a moisture content by weightof oven dry material of substantially 76% at a temperature ofapproximately 165, for approximately 30 minutes, spraying thepre-hydrolized material in a blow cyclone, de-moisturizing the materialto a consistency of substantially 11% of the oven dry Weight ofmaterial, compressing the material to increase the consistency to 36%,shredding the compressed material, passing the material through analkaline cooking step in a continuous digester with an aqueous digestingagent comprising NaOH and Na2S in a ratio of approximately 9 to 1 withthe combined amount of digester chemical equaling substantially 13.6% ofthe oven dry weight of the plant material and having a suldity ofapproximately 27.7% and digesting the material at a temperature ofapproximately C. for approximately 18 minutes.

References Cited in the tile of this patent UNITED STATES PATENTS1,931,575 De La Roza Oct. 24, 1933 2,625,474 Atkinson Ian. 13, 1953FOREIGN PATENTS 210,740 Austraua oct. 9, 1957 OTHER REFERENCES Ind. &Eng. Chem., vol. 6, No. 10, pp. 1 and 2, May 20, 1928.

1. A CONTINUOUS PROCESS FOR PULPING OF FIBROUS, NONWOODY,LIGNO-CELLULOSE CONTAINING PLANT MATERIALS WHICH COMPRISES THE STEPS OFSCREENING THE MATERIAL TO REMOVE A PROPORTION OF THE DIRT, DUST ANDPITH-TYPE MATERIAL THEREIN; PRE-HYDROLYZING THE SCREENED MATERIAL WITH AMOISTURE CONTENT BY WEIGHT OF OVEN DRY MATERIAL OF FROM 65% TO 90% FORNOT LESS THAN FIVE MINUTES NOR MORE THAN 50 MINUTES AT A TEMPRATURE NOTLESS THAN 140* C. AND NOT MORE THAN 190* C.; SPRAYING THE PRE-HYDROLYZEDMATERIAL IN A BLOW CYCLONE; DE-MOISTURIZING THE MATERIAL; COMPRESSINGTHE MATERIAL AND SUBSEQUENTLY SHREDDING THE COM-